Light source with non-white and phosphor-based white LED devices, and LCD assembly

ABSTRACT

A light source incorporates phosphor- based white  light emitting diodes (LEDs). The LEDs may be raised off the floor of the optical cavity to permit light to be emitted from the base of the LED. Additionally, a reflective protrusion may be placed beneath the raised LED to aid in redirecting light forward. The LEDs may be skewed in relation to adjacent LEDs to reduce interference. Non-white LEDs may be incorporated into the light source to permit for selective color tuning. Fluorescent lamps may also be implemented in combination with the LEDs to form a hybrid light source. The light source may be used as a backlight for a liquid crystal display assembly.

Notice: More than one reissue application has been filed for the reissueof U.S. Pat. No. 6,666,567. The reissue applications are applicationSer. No. 11/788,399 (the present application), Ser. No. 11/788,398(filed concurrently herewith), and Ser. No. 11/316,597, all of which aredivisional reissues of U.S. Pat. No. 6,666,567.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention generally relates to lighting systems, and moreparticularly, to light sources implementing light emitting diodes(LEDs).

2. Background

Many industries and applications need backlighting to illuminate aninformation source. In particular, transmissive liquid crystal displays(LCDs) have become very popular in many electronic media. LCDs areuseful in applications such as, but not limited to, displays inavionics, laptop computers, video cameras, and automatic teller machinedisplays. However, many LCDs require backlighting to illuminate theinformation being displayed.

Many systems perform the backlighting function in conventional displays.For example, one way to backlight an information source employs an arrayof conventional straight tubular fluorescent lamps. While theseconventional lamps are inexpensive and do not require complex electroniccontrols, they are sometimes inadequate for particular applications. Forinstance, in avionics applications, the poor color quality of thephosphors and the short lamp life of these conventional lamps, amongother shortcomings, limit their usefulness.

To avoid the various problems with conventional lamps, manymanufacturers employ customized lamps, such as tubular serpentine lamps.Unlike conventional fluorescent lamp arrays, custom-made serpentinelamps commonly provide good color characteristics, light luminanceuniformity, and long lamp life. These lamps are typically hand made, andconsequently, are comparatively costly. Moreover, these lamps. areextremely fragile and difficult to install. Therefore, while custom-madetubular serpentine lamps may meet certain standards for the backlightingfunction, the high cost and fragility associated with these lampsdetract from the advantages they offer.

A third alternative for backlighting information sources is flatfluorescent lamps. An exemplary flat fluorescent lamp, described in U.S.Pat. No. 5,343,116, issued Aug. 30, 1994, to Winsor, comprises asubstrate fritted to a transparent cover lid, forming an enclosure.Diffuse channels are formed into the substrate in the interior of theenclosure. Standard phosphors are added to the interior of the enclosurewhich is further flushed with a material for emitting energy, such asargon or mercury. Energy is emitted in the form of visible light when anelectric potential is introduced to the lamp by two electrodes, with oneelectrode placed at each end of the diffuse channel. Such lampspotentially offer greater ruggedness and lower manufacturing costs thanserpentine tubular lamp alternatives. However, these lamps are stillcostly to manufacture and are difficult to repair.

Yet another alternative for backlighting information sources implementsLEDs. The use of LEDs as light sources can be advantageous for severalreasons. LEDs have a long life, which reduces the frequency forreplacing non-functioning diodes. Further, when it is time to replace anLED, replacement is easier and more cost effective than when replacing afluorescent light source. Additionally, LEDs are mechanically robust,i.e., they can typically withstand greater shocks and vibration thanconventional fluorescent lights. Referring now to FIGS. 1 and 2, aconventional light source 100 incorporating LEDs comprises an opticalcavity 102, multiple LEDs 104, a power source (not shown), and adiffuser 106 (FIG. 2). Optical cavity 102 has a floor 108 in theinterior portion of light source 100 and an exterior surface 110.

As shown in FIG. 2, in conventional LED light systems, the LEDs 104 areattached directly to the floor 108 of the optical cavity 102. Referringto FIG. 3, LED 104 typically comprises a surface mount deviceconstructed by encasing a diode 300 near the center of a smalltranslucent rectangular block 302. Electrical contacts 304 and 306 atthe ends of block 302 connect to the diode via a small lead frame 308.

Conventional LED lighting systems, however, fail to perform adequatelyfor many backlighting applications, such as avionics, in which strictdisplay performance requirements restrict their use. For example, LEDstypically use power less efficiently than conventional fluorescent lampsto produce comparable light intensity. Further, a conventionalfluorescent lamp relies on phosphors which have narrowly definedspectral emission peaks that must be carefully controlled to providerepeatable color output. Control of the phosphor mixture to produceproduction-quality lamps requires significant investment of time andeffort to maintain a uniform mixture, produce an acceptable color point,and ensure color purity based on phosphor chemistry. Moreover, inconventional white LEDs, the spectral emission is dominated by the bluespectral emission, and thus, the resulting “white” light is heavilyshifted toward the blue spectrum. This shift limits the usefulness ofLED light sources in backlighting applications.

SUMMARY OF THE INVENTION

A light source according to various aspects of the present inventioncomprises LEDs raised above the floor of the optical cavity. The raisedLEDs may optionally have a protrusion under the LED for assisting inredirecting light. In another embodiment, adjacent LEDs may be skewedrelative to one another to reduce absorption and reflection among theLEDs. In a further embodiment, non-white LEDs may be incorporated intothe light source to permit selective color tuning. In an alternativeembodiment, a hybrid light source may be created when fluorescent lampsare augmented with LEDs. These LEDs, which may optionally be raisedabove the floor of the optical cavity, may also optionally have aprotrusion beneath. the raised LED.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention is particularly pointed out anddistinctly claimed in the concluding portion of the specification. Theinvention, however, both as to organization and method of operation, maybest be understood by reference to the following description taken inconjunction with the claims and the accompanying drawings, in which likeparts may be referred to by like numerals:

FIG. 1 is plan view of a prior art light source incorporating LEDtechnology;

FIG. 2 is a side cross-sectional view of the light source of FIG. 1;

FIG. 3 is a perspective view of a conventional diode;

FIG. 4. is a perspective view of an elevated diode in accordance with anexemplary embodiment of the present invention;

FIG. 5 is plan view of a light source implementing LEDs in accordancewith an exemplary embodiment of the present invention;

FIG. 6 is a side cross-sectional view of the light source of FIG. 5;

FIG. 7 is a side cross-sectional view of the light source of FIG. 5having protrusions beneath the raised LEDs in accordance with a furtherembodiment of the present invention;

FIG. 8 is a plan view of a light source configuring LEDs in anorthogonal arrangement in accordance with an exemplary embodiment of thepresent invention;

FIG. 9 is a plan view of a light source configuring LEDs in an obliquearrangement in accordance with an exemplary embodiment of the presentinvention;

FIG. 10 is a plan view of a hybrid light source incorporating LEDs andtubular fluorescent lamps in accordance with an exemplary embodiment ofthe present invention;

FIG. 11 is a plan view of a hybrid light source incorporating LEDs andU-shaped fluorescent lamps in accordance with an exemplary embodiment ofthe present invention;

FIG. 12 is a plan view of a hybrid light source incorporating LEDs and aserpentine fluorescent lamp in accordance with an exemplary embodimentof the present invention; and

FIGS. 13-15 are plan views of further embodiments of hybrid light sourceconfigurations in accordance with various aspects of the presentinvention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The ensuing descriptions are preferred exemplary embodiments only, andare not intended to limit the scope, applicability, or configuration ofthe invention in any way. Rather, the ensuing descriptions provide aconvenient description for implementing various exemplary embodiments oflight sources according to various aspects of the present invention, itbeing understood that various changes may be made in the function andarrangement of elements described in the preferred embodiments withoutdeparting from the spirit and scope of the invention as set forth in theappended claims.

Referring now to FIGS. 4-6, a light source 500 in accordance withvarious aspects of the present invention implements an LED that is notflush with floor of the optical cavity. Raising LEDs 504 above thesurface tends to capture rear-emitted light that is otherwise absorbedor otherwise lost, enabling the light source to emit more light withoutadditional power. In the present embodiment, the light source 500comprises: a housing 501 having a floor 410 and an exterior wall 503forming an optical cavity 502; multiple LEDs 400; and a power source(not shown). The light source may further include a diffuser 516 (FIG.6). Housing 501 may be constructed of any suitable material according tothe criteria of the application, such as heat exposure, mechanical shockresistance, or cost. In the present embodiment, the housing 501comprises aluminum, steel, glass, or ceramics, and defines the opticalcavity 502. The optical cavity comprises any cavity defined in thehousing in which light is to be dispersed. The floor 410 and or wall 503may optionally be coated with a reflective material, for example,Duraflect™, expanded polytetrafluoroethylene, or any diffuse white paintsuch as a polyurethane paint. The floor 410 comprises any suitable baseor surface for supporting the LEDs 400 or other relevant components.

The power source provides appropriate power supply and control tooperate the lamp. The power source may provide power in any appropriateform, such as AC electrical current, and may control the power in anysuitable manner, for example in conjunction with a voltage source withcurrent limiting resistance, a constant current source, or a pulse widthmodulated current source,

LED 400 may be any LED suitable for the application, such as aphosphor-based white LED sold by Nichia Corp, Tokushima, Japan. Thecolor, type, configuration, performance, and other characteristics maybe selected according to any appropriate criteria. In the presentembodiment, LED 400 includes a diode 402 encased in a translucentrectangular package 404. The LED 400 is raised by a support system 405such that the base of LED 400 is elevated above the floor 410 of opticalcavity 502. For example, the support system 405 suitably comprises apair of L-brackets 406 and 408 attached to either side of the LED 400 tosupport the LED 400 above the floor 410. L-brackets 406 and 408 may beaffixed to floor 410 according to any suitable technique, such as by anadhesive, fastener or solder. Any support system 405 that raises the LED400 above floor 410, for example, by using raised, a support matrix, orthe like, may be used to support the LED 400.

The support system 405 may further connect the LED 400 to the powersource. For example, in the present embodiment, the L-brackets 406 and408 may be constructed of a suitable electrically conductive materialthat supports the, LED above the surface of the floor 410, such ascopper or beryllium. A lead frame 412 electrically connects the diode402 with L-brackets 406 and 408. L-brackets 406 and 408 are suitablyconnected to a printed circuit board which is connected to the powersource, for example through control electronics.

In configurations where LEDs 400 are raised above floor 410, as in FIGS.5 and 6, the light output of the light source may be furtheraccomplished by providing a reflective protrusion beneath the raisedLEDs 504, further optimizing the recapture of emitted light. By placingthe protrusions under the raised LEDs 504, a greater amount of light maybe redirected forward, causing a greater light output without requiringa corresponding increase in power. Referring to the exemplary embodimentof FIG. 7, light source 700 has an optical cavity 502 above which LEDs504 are mounted, suitably by L-brackets 512 and 514. Protrusions 518 arelocated approximately below LEDs 504. Protrusions 518 may be prepared inany suitable manner and shape, such as according to the desiredapplication. For example, protrusions 518 may be prepared by stampingthe floor 410 of the optical cavity 502 such that protrusions 518 formin the surface of the floor 410. Alternatively, protrusions 518 may beconstructed by adding materials onto floor 410, for example, by placingdroplets of an epoxy material onto floor 410 and then covering thesurface of the epoxy with a reflective material. Protrusions 518suitably have an approximately parabolic or semi-spherical shape that isconvex relative to the floor 410 of optical cavity 502. Further,protrusions 518 may alternatively be shaped to direct in a predetermineddirection. This configuration may be useful in applications having anarrow range of desired viewing angles for an associated display.

In accordance with various aspects of the present invention, the lightemitted by the light source may be further enhanced by arranging theLEDs in an array that reduces any absorptive or reflective effects ofadjacent LEDs. For example, referring to FIG. 8, in accordance with afurther embodiment of the present invention, a light source 800 has anoptical cavity 802 with a floor 804. The longitudinal axes of a firstset of LEDs are oriented in a first direction, such as horizontally 806,and those of a second set of LEDs are oriented in a second direction,such as vertically 808, such that they are perpendicular to one another.This orthogonal arrangement of adjacent LEDs, due to the relativeplacement of neighboring LEDs, tends to reduce the absorptive orreflective effect that adjacent LEDs may have on each other, permittinga greater light output without requiring an additional power input.Further, any or all of the LEDs may be mounted either directly ontofloor 804, or alternatively, may be mounted above floor 804 as describedabove. Additionally, protrusions, as described above in accordance withFIG. 7, may be added to further enhance the recapture of rear-emittedlight. Therefore, by skewing orientation of the LEDs relative to oneanother, the intensity of the light provided by the light source tendsto increase without requiring a corresponding increase in power. Lightoutput may be further enhanced by raising the LEDs above the opticalcavity floor.

Several variations in the orientation of the LEDs may be implemented toenhance light output. For example, referring now to FIG. 9, inaccordance with yet another embodiment of the present invention, lightsource 900 has an optical cavity 902 with a floor 904. Three sets ofLEDs are oriented in three different directions, such as vertically 908and at approximately 45° from the vertical 906, 910. Due to the relativeplacement of neighboring LEDs, this oblique configuration also tends toreduce the absorptive or reflective effects of adjacent LEDs, yieldingimproved output without requiring additional power. Further, inaccordance with other aspects of the present invention, any or all ofthe LEDs may be mounted either directly onto floor 904, oralternatively, may be mounted above floor 904 as described above.Additionally, protrusions, as described in accordance with FIG. 7, maybe added to further enhance the recapture of rear-emitted light.

A light source according to various aspects of the invention may furtherbe configured to exhibit improved spectral characteristics. Inaccordance with a further embodiment of the present invention, non-whiteLEDs, preferably, red, green, and blue LEDs, and more preferably red andgreen LEDs, may be incorporated into the light source as described andconstructed in FIGS. 4-15 to enable it to have a tunable color output.Non-white LEDs, in particular red, green and blue LEDs may be anycommercially available non-white LED.

The non-white LEDs may be configured in the light source in a variety ofmanners, including, but not limited to, clustering the different LEDtypes together, and by laying down each color in separate rows. Further,non-white LEDs may be randomly dispersed throughout the light sourcewith white LEDs, and may also be used in combination with fluorescentlamps as described below. The non-white LEDs may be mounted directly onthe floor of the optical cavity, or as described in detail above, orthey may be elevated above the optical cavity floor, and further, theymay optionally be elevated above reflective protrusions as describedabove.

By incorporating non-white LEDs, multiple-wavelength LED light sourcesare introduced into a diffuse optical cavity to allow color mixing, withthe purpose of increasing the color saturation of an LED-based backlightto increase its usefulness in lighting an LCD panel. These emissionspectra allow tuning of the color balance of the backlight by activelydriving the LEDs or selectively enhancing particular colors to achieve adesired balance. This tunability allows one LED backlight to be usedwith a wide variety of LCD panels possessing different combinations ofcolor filters. It also allows active tuning of the color balance of anLED-based light source across the color spectrum, limited only by thesaturation of the individual color elements comprising the backlight.

-   -   To exploit the advantages of both LEDs and fluorescent light        sources, a hybrid light source may incorporate both LEDs and        fluorescent lights. Referring to FIG. 10, in accordance with an        exemplary embodiment according to various aspects of the present        invention, a light source 1000 has an optical cavity 1002        containing alternating rows of tubular fluorescent lamps and        LEDs. An optional reflective cavity 1028 may be added to the        light source to further enhance light output. In accordance with        this exemplary embodiment, six tubular fluorescent lamps 1004,        1006, 1008, 1010, 1012, and 1014 are arranged in a parallel        configuration within the optical cavity 1002. The fluorescent        lamps may be mounted in any suitable manner, for example, by        using a support to mount the fluorescent lamp in optical cavity        1002. Fluorescent lamps 1004, 1006, 1008, 1010, 1012, and 1014        may be any commercially available tubular fluorescent lamp.        These lamps may be either hot cathode or cold cathode lamps and        may have a variety of shapes, including, but not limited to,        straight, U-shaped (e.g., as elements 1106, 1108, and 1110 are        illustrated in the exemplary embodiment shown in FIG. 11), and        serpentine fluorescent lamps (e.g., as element 1206 is        illustrated in the exemplary embodiment shown in FIG. 12).

LEDs may be interspersed among the fluorescent lamps in a variety ofconfigurations in the hybrid light source. As seen in FIG. 10, rows ofLEDs 1018, 1020, 1022, 1024, and 1026 are alternated in between thefluorescent lamps 1004, 1006, 1008, 1010, 1012, and 1014. LEDs may bewhite LEDs, non-white LEDs, or may be a mixture of both white andnon-white LEDs as described above. Further, the LEDs may be mounteddirectly to the floor 1030 of the optical cavity 1002, or may be mountedabove the optical cavity 1002 as shown in FIG. 4, and may further bemounted over reflective protrusions as described above. Further, theLEDs may be mounted in skewed directions relative to adjacent LEDs asdescribed in FIGS. 8 and 9.

It should be appreciated that the present invention is not limited tothe configurations described above. For example, referring to FIGS.13-15, various alternative embodiments may include an edge-litconfiguration, i.e., light floods the cavity from the sides and israndomly reflected. In the edge-lit configurations, the LEDs suitablyface into the cavity, and not toward the view.

Referring now to FIGS. 13 and 14, these figures illustrate light sourceembodiments having the illumination sources around the perimeter of thelamp. In FIG. 13, light source 1300 has LED rows 1302 and 1304 onopposite sides 1312 and 1314 of optical cavity 1306. Fluorescent lamps1308 and 1310 are also located on opposite sides 1316 and 1318 ofoptical cavity 1308. In FIG. 14, light source 1400 has LEDs 1402 aroundthe perimeter of optical cavity 1404. Fluorescent lamps 1406 and 1408are on opposite side 1410 and 1412 of optical cavity 1404 The LEDs 1302,1304 and 1402 of FIGS. 13 and 14 may be in a variety of orientations,including skewed relative to one another, raised from the optical cavitysurface, and having a protrusion under the elevated LED. Further, avariety of LED color combinations may be implemented to permit selectivecolor tuning

Referring now to FIGS. 13 and 14, these figures illustrate light sourceembodiments having the illumination sources around the perimeter of thelamp. In FIG. 13, light source 1300 has LED rows 1302 and 1304 onopposite sides 1312 and 1314 of optical cavity 1306. Fluorescent lamps1308 and 1310 are also located on opposite sides 1316 and 1318 ofoptical cavity 1306. In FIG. 14, light source 1400 has LEDs 1402 aroundthe perimeter of optical cavity 1404. Fluorescent lamps 1406 and 1408are on opposite side 1410 and 1412 of optical cavity 1404. The LEDs1302, 1304 and 1402 of FIGS. 13 aid 14 may be in a variety oforientations, including skewed relative to one another, raised from theoptical cavity surface, and having a protrusion under the elevated LED.Further, a variety of LED color combinations may be implemented topermit selective color tuning.

It should be appreciated that in all embodiments of the presentinvention any number of LEDs and fluorescent lamps may be used accordingto the particular application or design criteria of the backlight or thedisplay. As such, the drawing figures and the present description areonly meant to illustrate exemplary embodiments in accordance with thepresent invention and are not intended to limit the invention to theconfigurations illustrated herein.

Thus, a light source incorporating LEDs and fluorescent lamps accordingto various aspects of the present invention provides several featuresand advantages, such as light output uniformity. In addition, the abovedescriptions are preferred exemplary embodiments only, and are notintended to be limiting in any way. Various modifications,substitutions, and other applications of the present embodiments may bemade without departing from the spirit and the scope of the invention asset forth in the appended claims.

1. A light source, comprising: an optical cavity having a floor; atleast one light emitting diode (LED) having a top and a bottom coupledto said floor such that said bottom of said at least one light emittingdiode is elevated above said floor of said optical cavity; and areflective protrusion located below said at least one LED.
 2. A lightsource comprising: an optical cavity having a floor; at least onefluorescent lamp coupled to said optical cavity; and at least two LEDscoupled to said optical cavity, wherein adjacent said at least two LEDsare skewed at approximately 45° relative to one another.
 3. A lightsource comprising: an optical cavity having a floor; at least onefluorescent lamp coupled to said optical cavity; and at least two LEDscoupled to said optical cavity, wherein adjacent said at least two LEDsare perpendicular to one another.
 4. A light source comprising: anoptical cavity having a floor; at least one fluorescent lamp coupled tosaid optical cavity; and at least one LED coupled to said opticalcavity, wherein said at least one LED is coupled with said opticalcavity such that said LED is elevated from said floor of said opticalcavity.
 5. A light source according to claim 4 further comprising aprotrusion on said floor positioned beneath said elevated LED.
 6. Alight source comprising: an optical cavity having a floor; at least twofluorescent lamps coupled to said optical cavity; and at least one LEDcoupled to said optical cavity, wherein two of said fluorescent lampsare located at opposing sides of said optical cavity, and said LEDs arelocated at intervals around substantially the perimeter of said opticalcavity.
 7. A method of manufacturing a light source comprising the stepsof: providing an optical cavity having a floor; mounting at least oneLED having a top and bottom in said optical cavity such that said bottomof said LED is elevated above said floor of said optical cavity; andproviding a protrusion below said at least at one LED.
 8. A method ofmanufacturing a light source comprising the steps of: providing anoptical cavity having a floor; mounting at least one LED having a topand bottom in said optical cavity such that said bottom of said LED iselevated above said floor of said optical cavity; and mounting at leastone fluorescent lamp in said optical cavity.
 9. A light sourcecomprising: an optical cavity having a floor; a plurality of fluorescentlamps coupled to said optical cavity substantially parallel to oneother; and a plurality of LEDs coupled to said optical cavityinterspersed among said fluorescent lamps, wherein said plurality ofLEDs are coupled to said optical cavity, said plurality of LEDs havingtops and bottoms and being coupled to said optical cavity such that saidbottoms of said LEDs are elevated above said floor.
 10. A light sourcecomprising: an optical cavity; a plurality of first light-emittingdiodes each of which is a phosphor light-emitting diode that emits whitelight, each first light-emitting diode comprising a diode encased in alight-transmitting package; a plurality of second light-emitting diodeseach of which emits non-white light, each second light-emitting diodecomprising a diode encased in a light-transmitting package; wherein thefirst and second light-emitting diodes are arranged to emit light intothe optical cavity such that mixing of spectral outputs from the firstand second light-emitting diodes occurs in the optical cavity.
 11. Alight source of claim 10, further comprising at least one thirdlight-emitting diode having a spectral output different from those ofthe first and second light-emitting diodes.
 12. A light source of claim11, wherein the spectral output of the second light-emitting diodes is ared output.
 13. A light source of claim 11, wherein the spectral outputof the third light-emitting diode is a green output.
 14. A light sourceof claim 13, further comprising at least one fourth light-emitting diodehaving a blue output.
 15. A liquid crystal display assembly comprising:a backlight including: an optical cavity; a plurality of firstlight-emitting diodes each of which is a phosphor light-emitting diodethat emits white light, each first light-emitting diode comprising adiode encased in a light-transmitting package; a plurality of secondlight-emitting diodes each of which emits non-white light, each secondlight-emitting diode comprising a diode encased in a light-transmittingpackage; wherein spectral outputs of the first and second light-emittingdiodes are operative to tune a color balance of the backlight; whereinthe first and second light-emitting diodes are arranged to emit lightinto the optical cavity such that mixing of the spectral outputs fromthe first and second light-emitting diodes occurs in the optical cavity;and a liquid crystal display panel positioned adjacent to the backlightso as to be illuminated by the backlight.
 16. A liquid crystal displayassembly of claim 15, further comprising at least one filter that isconfigured to be used with the liquid crystal display panel and thebacklight.